As a method of giving conductivity or metallic luster to a nonconductor product, there have been known a method of depositing metal to the nonconductor product in vacuum, a method of sputtering metal to the same, a method of electroless plating on the same, and the like. Electroless plating is a method of chemically reducing and depositing metal ions in a solution to make a metallic coating form on the surface of the material, even on the surface of an insulating material including a resin and the like, which is different from electroplating in which a metal coating is electrolytically deposited by electricity.
Plated coatings formed by electroless plating, however, have the problem of not having sufficient adherent strength to the surface of the material. Therefore, when electroless plating is carried out, there have been known, as pretreatment thereof, methods of electroless plating such as surface roughening in which the surface of a nonconductor product is chemically etched, with the addition of a polar group and treatment by a catalyst. Treatments of surface roughening and addition of the polar group are mainly carried out with chemicals including chromic acid, permanganic acid, and sulfuric acid and the like. These chemicals have a problem that they become a cause of environmental pollution and cost a huge sum for treatment of the waste liquid. Further, surface roughening and addition of the polar group are performed with a treatment by plasma or corona discharge and the like. As the treatment by plasma or corona discharge and the like should be generally done in a vacuum, there becomes a problem in the productivity, and the development of alternative treatment methods have been sought.
As a method of electroless plating on a resin product, Japan Patent Laid-Open Publication No. 1-092377 discloses a method in which a resin molding is pretreated with ozone gas and is then treated with electroless plating. According to the same publication, unsaturated bonds on the surface of resin are cleaved by ozone gas to turn into low molecules, molecules with different compositions coexist on the surface, depriving smoothness from the surface to make it rough. The same publication thus describes that the coating formed with electroless plating penetrates well into the rough surface without being stripped off easily.
In the method described above, adherent strength of the plated coating is improved by roughening the resin surface, namely, by a so-called anchoring effect. In the method of roughening the surface, however, the smoothness thereof is lowered, so that, in order to obtain a surface with a metallic luster having a high-grade design performance, the plated coating needs to be thickened, which causes a disadvantage of an increased number of man-hours.
Japan Patent Laid-Open Publication No. 8-253869 thus discloses a method in which electroless plating is performed after ultraviolet rays are irradiated on a resin surface. With this method, the resin surface is activated by ultraviolet radiation, and active groups on the activated resin surface chemically bond with the molecules of metal which is the material for plating, making the adherent strength of the plated coating improved. Further, as the resin surface is not easily roughened, a metallic luster having a high-grade design performance can be obtained.
Japan Patent Laid-Open Publication No. 10-88361 further discloses a method in which electroless plating is performed in such a way that, after ultraviolet rays are irradiated on a resin molding as a pretreatment for electroless plating, the resin molding is contacted with an alkali solution containing a nonionic surfactant having a polyoxyethylene linkage. Also with this method, as the resin surface is activated by ultraviolet radiation and is not easily roughened, a metallic luster having high-grade design performance can be obtained.
In the meantime, a light source for ultraviolet radiation generates not only ultraviolet rays but also infrared and far-infrared rays. In addition, in order to activate a resin surface, a large quantity of energy as well as radiation for a relatively long period of time is necessary. A large quantity of heat is thus applied to the resin molding from the light source at the time of ultraviolet radiation, which may disadvantageously cause deformation of the resin molding by heat in some types of resin. Further, in some forms of the resin molding, a shadowed section from ultraviolet radiation is made due to being situated in a dead area of the light axis, which may make it difficult to irradiate ultraviolet rays onto the shadowed section.
According to a study made by the present inventors, on the other hand, when the dosage of ultraviolet irradiation is too much, it is evidently observed that the adherent strength of the plated coating, on the contrary, lowers.
As a method of giving a metallic luster to a nonconductor product, the methods as described above may satisfy the need in some cases, but according to the usage of the nonconductor product, further electroless plating or electroplating thereon may be required when a higher endurance and fanciness is required.
The present invention is made in view of the situation described above, and the object of the present invention is; firstly, to provide a method of plating a nonconductor product in which, when the nonconductor product is pretreated by electroless plating, the plated nonconductor product with the plated layer and the surface of the nonconductor product being tightly adhered to each other can be obtained without causing any problems such as environmental pollution and treatment of the waste liquid; secondly, to provide a method of plating a nonconductor product in which, when a resin product is pretreated as an object to be plated by electroless plating using ultraviolet radiation, deformation of the resin product by heat can be prevented and the adherent strength of the plated coating can be further improved; thirdly, to provide a method of plating a nonconductor product in which a plated coating with a higher endurance and fanciness can be formed thereon; and fourthly, to provide the plated nonconductor product obtained by these methods.